Every year about this time I like to remind our students to be careful crossing the street. Some back-of-the envelope calculations we did once upon a time suggest that the time change is a very dangerous time for walkers at dusk. (It is also true that it is now safer in the morning, but I’m not sure I want to counsel you to be less safe in the morning).

“The change that’s going to occur on Sunday is going to have some pronounced effects on your risks of walking between 5 p.m. and 7 p.m.,” Dr. Gerard said last night. “Basically, these are the hours when it’s just getting dark. Next week at this time, it will be pitch black. But people walking and people driving won’t have adjusted. The baseline risk for getting killed is almost tripled.”

Their study of pedestrian fatalities from 1999-2005 shows that there is an average of 37 more U.S. pedestrian deaths around 6 p.m. in November compared to October. That amounts to an increase of 186 percent.

No such jump was seen for drivers or passengers in cars.

“It’s astonishing,” Dr. Gerard said of the data. “It’s particularly worse right at the switch date, [when the average increases] two people a day for the next couple weeks, until the adjustment is made.”